The D-backs have fallen in the prospect rankings the past four months, but the reason for the drop is because some of those top prospects have graduated to contribute at the big league level.

It's certainly fair to wonder just where the D-backs would be without the contributions they've received from prospects like shortstop Didi Gregorius, outfielder A.J. Pollock and pitchers Tyler Skaggs and Randall Delgado.

Despite the promotions, which caused their standing in the overall rankings to fall, the D-backs feel good enough about the prospects left that they have not rushed to make a deal leading up to the July 31 non-waiver Trade Deadline.

"I still have a lot of confidence in the players that are here in our system," GM Kevin Towers said when discussing possible trades. "I like the depth we have in our system."

Prospect rankings are one measure of the strength of a team's system. Another that's probably more telling is the amount of interest those prospects receive from other teams.

"We're always asked about a number of guys in our system," Towers said, without naming specific players. "There's a lot of interest in them."

Graduated

Skaggs was the D-backs' top prospect heading into the season, and after a slow start at Triple-A Reno, he found his form and has pitched well in three separate stints with the D-backs.

Gregorius, who was Arizona's third-ranked prospect in the preseason, began the year on the disabled list. When he did make his D-backs debut April 18 at Yankee Stadium, he hit the first pitch he saw for a home run.

While most observers had Pollock, the team's eighth-best preseason prospect, beginning the season in Reno, injuries helped him make the Opening Day roster. Pollock's performance since, particularly his outstanding defense in center, has kept him in the big leagues.

Dropped off

Aside from those players who were promoted to the big leagues, Chase Anderson, the 20th-ranked preseason prospect, slipped enough to fall off the list. The 25-year-old right-hander had posted a 3-7 record and 5.37 ERA in 14 games (12 starts) during his first season with Triple-A Reno.

New faces

Right-handers Braden Shipley and Aaron Blair joined the prospect list after being drafted this past June. In addition, infielder Brandon Drury and right-hander Felipe Perez also joined the D-backs' Top 20.

Shipley, who played at the University of Nevada, was taken with the No. 15 overall pick, while Marshall University's Blair was selected 36th overall in the Competitive Balance Round.

Drury was overlooked when he came over from Atlanta in the Justin Upton deal in January, but a hot start at Class A South Bend has made some take a second look.

Perez was signed by the D-backs last August just before he was to begin classes at UCLA. Perez had gone undrafted two months before that.